Window wall is a term generally used in the construction industry to describe a window system that spans between floors of a building, for example, from a top of a bottom floor slab to the underside of an above floor slab. Sill and head receptors are installed using anchors or embeds and shims to tightly set the receptors parallel to one another on the same plane and at the correct height to accept the unitized window panels. Below the sill receptor and above the head receptor, a gap exists where receptors have been shimmed to level, and a weather seal caulk is applied to both the exterior and interior sides of the receptors to seal the gaps between the slab and receptors from air and water infiltration. In window wall systems using vertical terminations, a jamb receptor is used to receive a unitized panel. Caulk is also applied to any gaps behind the jamb receptors.
Some existing window wall systems include a slab edge cover, which is an extruded or formed profile that clips, hooks or is fastened to the head receptor and the sill receptor along the entire length of the window system. In window wall systems that include slab edge covers, the slab edge covers may not be used at balcony conditions or in areas that an architect or designer wants exposed substrate, for example. The slab edge covers can be constructed from aluminum, glass, stone, or any suitable material. The slab edge covers can be installed from the interior with the window panels, or after the window panels are installed by using scaffolding and mounting the slab edge covers from the exterior.
During installation of an exemplary existing window wall system, the bottom of the unitized panels are placed into the sill receptor at an upward projection, commonly referred to as a “chicken head,” that locks the panel into place by keying into the lower horizontal of the panel and notches cut into the bottom of the frame verticals. The chicken head includes gaskets, typically applied in the factory, which prevent air and water from entering the system at the sill. Sealants are also applied at the sill in critical areas to help in sealing the system.
After placing the unitized panel into the sill receptor, the panel is tipped forward and rotated into the head receptor extrusion and is stopped from tipping too far forward (away from the building) by an extruded arm in the head receptor that has a factory installed gasket. The arm makes contact with the top horizontal of the panel and the panel verticals, which have been notched out at the factory in the front to allow the glass to move beyond the arm. Another longer arm with a factory installed gasket in the head receptor extrusion creates a seal to the glass when the panel is tipped in place. When the panel is tipped into the vertical position, it is then slid in a direction toward another installed panel or jamb receptor, along the sill and head to interlock with the adjacent panel using a male/female connection extruded into the verticals of both panels. A separate L-shaped drive-on extrusion is driven into the interior side of the head receptor extrusion and locked into place by way of serrated teeth and leverage, holding the panel tightly into the head receptor. A factory installed gasket on the drive-on fits snugly against the panel's top horizontal and verticals to create a tight seal. Sealant is applied to critical areas to ensure a tight air and water seal.
The above-mentioned exemplary window wall installation process is repeated from the starting floor to the top of the building.
Unitized curtain wall differs from unitized window wall in a number of ways, with one of the most noticeable differences being the appearance from the exterior. A curtain wall panel is hung outside the building structure from an anchoring system located on top of, in front of, or immediately under the building floor slab or substrate. In many cases, embeds, which are anchor stabilizers placed in the concrete form work before the concrete is poured, are used. When the concrete cures, the embeds are encased in the concrete providing a secure means of connection to the window system. In curtain wall systems, embeds are typically necessary because of the extreme forces that curtain wall exert to the outer edge of the concrete slab, and are relatively expensive to provide when labor and material are considered. In most cases, each vertical mullion at each floor includes an embed and a connection. The connections may provide vertical and/or lateral support. In conditions where steel is used, the anchoring system is welded to the steel structure. Window wall generally does not require embeds as the system is deep enough into the building structure to support the lateral and vertical loads.
Because the curtain wall is held outside the buildings structure, a gap between the slab edge and the back of the curtain wall exists. Fire stopping material is used to fill the gap between the slab edge and the back of the current wall to prevent inter story jumping of flames and smoke in the event of a fire. The fire stopping is also relatively expensive to provide considering the cost of labor and material for installation at each slab edge/curtain wall condition. Window wall does not require fire stopping because the slab edge extends beyond the interior of the system.
In addition to inter story fire stopping, inter story sound proofing is also a concern with a curtain wall system. Although the fire safing insulation provides some sound absorption qualities, additional sound proofing to curtain wall gaps is typically needed to mitigate the migration of sound between floors of a building. Because curtain wall mullions extend between floors, the sound may also travel through the hollows of the mullions unless soundproofing is built into the system. Window wall systems do not require inter story sound proofing because the slab edge, which extends beyond the interior of the system, acts as the sound proofing.
Another disadvantage to curtain wall is that it is more difficult to transition to the inside of the building structure, as is needed for inset balcony conditions. Curtain wall has to change from a top hung system to a system that dead loads to the top of the slab, making it vulnerable to performance issues in those transitioned areas. Window wall is entirely dead loaded onto the slab and no special engineering is needed to bring the system deeper into the building structure. Further, window wall offers two silicone or other caulk chemical seals at each receptor, one on the interior and one on the exterior, ensuring a redundant barrier against air and water. Curtain wall relies on mechanical seals, in the form of gaskets, in most areas of its system.
In general, a curtain wall system requires more equipment, labor and specialized materials to install, than a window wall system. Since the panels of a curtain wall system are hung from above, the entire panel has to be lifted up to the connections above or dropped down with hoisting equipment from the floor above. Window wall is installed from the floor in which it will be placed and does not have to be lifted any further than the height of the sill.
To some architects and designers, curtain wall has a more appealing look than window wall, since curtain wall is mounted outside the building structure, the system does not require a protruding slab edge cover, giving it a smooth, flush faced look if it is a four-sided structurally glazed system. Although window wall systems can be aesthetically pleasing and perform well in thermal air and water testing, architects and designers at times desire a flush face system where the entire exterior is on the same vertical plane.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.